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n-dhcp4: don't fail dispatch in case of receive errors
Currently any error encountered in n_dhcp4_c_connection_dispatch_io() causes a dispatch failure and interrupts the library state machine. The recvmsg() on the socket can fail for different reasons; one of these is for example that the UDP request previously sent got a ICMP port-unreachable response. This can be reproduced in the following way: ip netns add ns1 ip link add veth0 type veth peer name veth1 ip link set veth1 netns ns1 ip link set veth0 up cat > dhcpd.conf <<EOF server-identifier 172.25.0.1; max-lease-time 120; default-lease-time 120; subnet 172.25.0.0 netmask 255.255.255.0 { range 172.25.0.100 172.25.0.200; } EOF ip -n ns1 link set veth1 up ip -n ns1 address add dev veth1 172.25.0.1/24 ip netns exec ns1 iptables -A INPUT -p udp --dport 67 -j REJECT ip netns exec ns1 dhcpd -4 -cf dhcpd.conf -pf /tmp/dhcp-server.pid If a client is started on veth0, it is able to obtain a lease despite the firewall rule blocking DHCP, because dhcpd uses a packet socket. Then it fails during the renewal because the recvmsg() fails: dhcp4 (veth0): send REQUEST of 172.25.0.178 to 172.25.0.1 dhcp4 (veth0): error -111 dispatching events dhcp4 (veth0): state changed bound -> fail The client should consider such errors non fatal and keep running. https://bugzilla.redhat.com/show_bug.cgi?id=1829178 https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/486
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@ -1136,6 +1136,13 @@ int n_dhcp4_c_connection_dispatch_timer(NDhcp4CConnection *connection,
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return 0;
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}
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/*
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* Returns:
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* 0 on success
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* N_DHCP4_E_MALFORMED if a malformed packet was received
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* N_DHCP4_E_UNEXPECTED if the packet received contains unexpected data
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* N_DHCP4_E_AGAIN if there was another error (non fatal for the client)
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*/
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int n_dhcp4_c_connection_dispatch_io(NDhcp4CConnection *connection,
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NDhcp4Incoming **messagep) {
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_c_cleanup_(n_dhcp4_incoming_freep) NDhcp4Incoming *message = NULL;
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@ -1150,10 +1157,11 @@ int n_dhcp4_c_connection_dispatch_io(NDhcp4CConnection *connection,
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connection->scratch_buffer,
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sizeof(connection->scratch_buffer),
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&message);
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if (r)
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if (!r)
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break;
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else if (r == N_DHCP4_E_MALFORMED)
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return r;
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break;
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return N_DHCP4_E_AGAIN;
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case N_DHCP4_C_CONNECTION_STATE_DRAINING:
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r = n_dhcp4_c_socket_packet_recv(connection->fd_packet,
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connection->scratch_buffer,
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@ -1161,8 +1169,10 @@ int n_dhcp4_c_connection_dispatch_io(NDhcp4CConnection *connection,
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&message);
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if (!r)
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break;
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else if (r != N_DHCP4_E_AGAIN)
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else if (r == N_DHCP4_E_MALFORMED)
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return r;
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else if (r != N_DHCP4_E_AGAIN)
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return N_DHCP4_E_AGAIN;
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/*
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* The UDP socket is open and the packet socket has been shut down
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@ -1180,18 +1190,21 @@ int n_dhcp4_c_connection_dispatch_io(NDhcp4CConnection *connection,
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connection->scratch_buffer,
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sizeof(connection->scratch_buffer),
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&message);
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if (r)
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if (!r)
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break;
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else if (r == N_DHCP4_E_MALFORMED)
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return r;
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break;
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return N_DHCP4_E_AGAIN;
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default:
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abort();
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return -ENOTRECOVERABLE;
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}
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r = n_dhcp4_c_connection_verify_incoming(connection, message, &type);
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if (r)
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if (r == N_DHCP4_E_MALFORMED || r == N_DHCP4_E_UNEXPECTED)
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return r;
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else if (r != 0)
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return N_DHCP4_E_AGAIN;
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if (type == N_DHCP4_MESSAGE_OFFER || type == N_DHCP4_MESSAGE_ACK) {
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n_dhcp4_c_log(connection->client_config, LOG_INFO,
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@ -1242,6 +1242,7 @@ int n_dhcp4_client_probe_dispatch_io(NDhcp4ClientProbe *probe, uint32_t events)
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return 0;
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}
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abort();
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return r;
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}
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